Abstract

Field experiments were carried out under natural conditions to compare the aboveground biomass, root growth and distribution, and topsoil nutrition contents ofswitchgrass (Panicum virgatum) and sainfoin (Onobrychis viciaefolia) grown in sole cropping and 2:1 row-replacement intercropping in semiarid loess region on Loess Plateau of northwest China. The sole and intercropping was compared based on the aboveground biomass, water use efficiency (WUE), soil organic matter (SOM) and total nitrogen (TN), and root biomass and distribution. Theaboveground biomass production was measured every year at the end of growth seasons in 2001 - 2005. Root biomass and vertical distribution were studied only in 2005. Topsoil SOM and TN contents were measured discontinuously during the study period. Results showed that intercropping reduced the aboveground biomass production of sainfoin significantly compared with its pure stand. The WUE of sole switchgrass was significantly the highest in each year among the three stands, while the intercropped stand was significantly higher than sole sainfoin on five-year averaged. The aggressivity of sainfoin to swichgrass decreased along with the growth years. Before 2005, the land equivalent ratio (LER) was bigger than 1.0 andactual yield loss (AYL) was positive. Under intercropping, root biomass input and root: shoot ratio in switchgrass reduced, while sainfoin inputs more photosynthate to root growth. Switchgrass had high root biomass and wide distribution vertically and horizontally indicates a higher belowground competitive ability in the mixture. It indicated a flexible distribution strategy of switchgrass tending to increase soil exploitation and space sequestration efficiency in soil layers. SOM and TN increased significantly for the three stands at the end of the fourth growth year, especially for the mixture. Switchgrass and sainfoin intercropped under 2:1 row-replacement can be a short-term rotation tillage choice with respect to soil management in the area.

Key words: aboveground biomass, competition, intercropping, root distribution, sainfoin, switchgrass.